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United States Patent |
6,181,397
|
Ichimura
|
January 30, 2001
|
Reflection-type liquid crystal display panel and method of fabricating the
same
Abstract
In a reflection-type liquid crystal display panel (10) provided with
reflective electrodes (13a), a reflective metal film (13a) is formed on an
insulating layer (12) having a surface provided with minute irregularities
(17) to form the reflective metal electrodes having surfaces of a shape
substantially complementary to the minute irregularities. Since the
surfaces of the electrodes (13a) are provided with minute irregularities,
external light incident on the liquid crystal display panel is not
reflected in a specular reflection mode, so that images are displayed on
the liquid crystal display panel in satisfactory visibility. The
insulating layer is formed by forming a positive photosensitive resin
layer on a back substrate (10a), exposing the positive photosensitive
resin layer to light through a transparent sheet (18) having a surface
provided with minute irregularities, and subjecting the exposed positive
photosensitive resin layer to a developing process. The thus fabricated
liquid crystal display panel is capable of suppressing reflection of
external matters therein and of displaying images in satisfactory
visibility. The insulating layer (12) underlying the electrodes (13a) is
patterned in a pattern similar to that of the electrodes (13a) to suppress
current leakage between the electrodes. A method of fabricating the
reflection-type liquid crystal display panel is also disclosed.
Inventors:
|
Ichimura; Koji (Tokyo-To, JP)
|
Assignee:
|
Dai Nippon Printing Co., Ltd. (Tokyo, JP)
|
Appl. No.:
|
048754 |
Filed:
|
March 25, 1998 |
Foreign Application Priority Data
| Apr 01, 1997[JP] | 9-96404 |
| Apr 01, 1997[JP] | 9-96405 |
Current U.S. Class: |
349/113; 349/138; 349/187 |
Intern'l Class: |
G02F 001/133.5; G02F 001/133.3; G02F 001/13 |
Field of Search: |
349/113,158,138,187
|
References Cited
U.S. Patent Documents
4861143 | Aug., 1989 | Yamazaki et al. | 349/138.
|
5321538 | Jun., 1994 | Maruyama et al. | 349/138.
|
5381256 | Jan., 1995 | Hanyu et al. | 349/138.
|
5500750 | Mar., 1996 | Kanbe et al. | 349/113.
|
5663778 | Sep., 1997 | Konno et al. | 349/138.
|
Primary Examiner: Sikes; William L.
Assistant Examiner: Ton; Toan
Attorney, Agent or Firm: Morgan & Finnegan LLP
Claims
What is claimed is:
1. A method of fabricating a reflection-type liquid crystal display panel
having a back panel comprising a flat back substrate, TFTs formed on an
inner surface of the back substrate, an insulating layer formed on the
inner surface of the back substrate, and reflective electrodes formed on
the insulating layer; said method comprising the steps of:
forming an insulating photosensitive resin layer on an inner surface of the
back substrate and drying the same;
exposing the photosensitive resin layer to light through a transparent
sheet having a surface provided with minute irregularities after drying
the photosensitive resin layer;
exposing the photosensitive resin layer to light through a photomask
provided with a contact hole pattern for forming contact holes;
subjecting the exposed photosensitive resin layer to a developing process
and drying the developed photosensitive resin layer to form an insulating
layer having a surface provided with minute irregularities (12m); and
forming a reflective metal film on the surface of the insulating layer
provided with the minute irregularities.
2. A method according to claim 1, wherein the transparent sheet having the
surface provided with the minute irregularities is a ground glass plate.
3. A method according to claim 1, wherein the minute irregularities include
ridges and valleys, and the height of the ridges of the minute
irregularities is in the range of 0.4 to 10 .mu.m.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflection-type liquid crystal display
panel and a method of fabricating the same. More particularly, the present
invention relates to a reflection-type liquid crystal display panel
suitable for use as a display unit for OA apparatus including note-size
lap top personal computers and word processors, video apparatus including
pocketable television sets, and game machines, and a method of fabricating
the same.
2. Description of the Related Art
The application of liquid crystal display panels to pocketable liquid
crystal television sets, lap top personal computers and word processors
has rapidly developed in recent years. Particularly, reflection-type
liquid crystal displays, which reflect incident external light to display
images, are being watched with keen interest because reflection-type
liquid crystal display panels do not need any backlight unit, are capable
of operating at a low power consumption rate and of being powered by
batteries; and are thin and of lightweight.
Generally known reflection-type liquid crystal display panels are TN liquid
crystal display panels in which a liquid crystal is driven in a twisted
nematic (TN) mode, and STN liquid crystal display panels in which a liquid
crystal is driven in a super twisted nematic (STN) mode. The TN liquid
crystal display panel displays monochromatic images by using the optical
properties of a liquid crystal display panel, namely, an optically
rotatory characteristic which is exhibited when no voltage is applied
thereto and a polarization canceling characteristic which is exhibited
when a voltage is applied thereto.
A dichromatic dye is added to a known amorphous chiral nematic guest-host
liquid crystal, and the orientation of the liquid crystal is controlled by
voltage to control the orientation of the dichromatic dye for displaying
images. A liquid crystal display panel employing such a mixture of an
amorphous chiral nematic guest-host liquid crystal and a dichromatic dye
does not need any polarizing plate, and has a high luminance and a wide
viewing angle.
A color liquid crystal display has a liquid crystal display panel provided
with an R-, a G- and a B-filter therein, and displays multicolor or
full-color images by utilizing an optical switching characteristic.
Currently, TN reflection-type liquid crystal display panels are employed
in portable liquid crystal television sets, namely, pocketable liquid
crystal television sets, driven in an active matrix driving mode or a
passive matrix driving mode.
Referring to FIG. 14 showing a conventional monochromatic reflection-type
liquid crystal display panel 20 in a typical sectional view, the liquid
crystal display panel 20 has a back glass substrate 20a, a front glass
substrate 20b disposed opposite to the back glass substrate 20a, an
insulating layer 22 formed on the inner surface of the back glass
substrate 20a, first electrodes 23a for forming pixels, formed on the
insulating layer 22 in the pattern of stripes, an alignment film 24a
formed on the insulating layer 22 so as to cover the first electrodes 23a,
second electrodes 23b formed on the inner surface of the front glass
substrate 20b in the pattern of stripes so as to extend perpendicularly to
the first electrodes 23a, and an alignment film 24b formed on the inner
surface of the front glass substrate 20b so as to cover the second
electrodes 23b. The second electrodes 23b formed on the front glass
substrate 20b are transparent electrodes, and the first electrodes 23a
formed on the back glass substrate 20a are reflective electrodes of a
conductive metal. The electrodes 23a and 23b of the glass substrates 20a
and 20b are scanned in a passive matrix driving mode to display images on
the liquid crystal display panel.
Referring to FIG. 15 showing a conventional monochromatic reflection-type
liquid crystal display panel 20 in a typical sectional view, the liquid
crystal display panel 20 has a back glass substrate 20a, a front glass
substrate 20b disposed opposite to the back glass substrate 20a, an
insulating layer 22 formed on the inner surface of the back glass
substrate 20a, thin-film transistors (TFTs) 21 forming pixels and formed
on the insulting layer 22, a matrix of electrodes 23a formed on the
insulating layer 22, an alignment film 24a covering the TFTs and the
electrodes 23a, a planar common electrode 23b formed on the inner surface
of the front glass substrate 20b, and an alignment film 24b formed on the
common electrode 23b. The common electrode 23b formed on the front glass
substrate 20b is a transparent electrode, and the electrodes 23a formed on
the back glass substrate 20a are reflective electrodes of a conductive
metal.
The back glass substrate 20a and the front glass substrate are spaced a
predetermined distance apart by a spacer, not shown, so as to form a space
therebetween, and a liquid crystal, such as a guest-host liquid crystal,
is filled in the space between the glass substrates 20a and 20b to form a
liquid crystal layer 25, and the liquid crystal layer 25 is sealed in the
space by a sealing member 26 attached to the peripheral parts of the glass
substrates 20a and 20b.
The conventional reflection-type liquid crystal display panel is provided
on its back surface with a reflecting plate of a metal, such as an
aluminum plate, having a surface finished by grinding to provide the same
with a light scattering property or a reflecting plate formed by
depositing a metal, such as aluminum, by evaporation on a roughened
surface of a base plate to provide the roughened surface with a light
scattering property to secure a wide visual angle. Usually, the reflecting
plate attached to the back surface of the liquid crystal display panel is
omitted if reflective electrodes are employed. The reflection-type liquid
crystal display panels 20 shown in FIGS. 14 and 15 are not provided with
any reflecting plate on their back surfaces.
The foregoing conventional reflection-type liquid crystal display panel
provided with the reflective electrodes having mirror surfaces reflects
images of matters in front of the reflection-type liquid crystal display
panel in a specular reflection mode and thereby the visibility of the
screen of the reflection-type liquid crystal display panel is
deteriorated.
SUMMARY OF THE INVENTION
Accordingly, it is a first object of the present invention to improve the
visibility of a reflection-type liquid crystal display panel provided with
electrodes having reflective surfaces by suppressing the reflection of
matters in front of the reflection-type liquid crystal display panel in
the reflective surfaces of the electrodes of the reflection-type liquid
crystal display panel.
The image displaying performance of the foregoing conventional
reflection-type liquid crystal display panel provided with the insulating
layer over the entire inner surface of the glass substrate is deteriorated
due to current leakage across the pixel electrodes if the insulating layer
has a low surface resistivity.
Accordingly, it is a second object of the present invention to improve the
image displaying performance of a reflection-type liquid crystal display
panel provided with electrodes formed on an insulating layer.
According to a first aspect of the present invention, a reflection-type
liquid crystal display panel comprises a flat, smooth substrate, an
insulating layer formed on the inner surface of the substrate, and
reflective electrodes formed on the insulating layer, in which the minute
irregularities are formed in the surfaces of the insulating layer, the
reflective electrodes are formed on the surface of the insulating layer so
as to conform to the minute irregularities.
According to a second aspect of the present invention, a reflection-type
liquid crystal display panel comprises a flat, smooth substrate, an
insulating layer formed on the inner surface of the substrate, and
reflective electrodes formed in a predetermined pattern on the insulating
layer, in which the insulating layer is formed in substantially the same
pattern as that of the reflective electrodes.
According to a third aspect of the present invention, a method of
fabricating a reflection-type liquid crystal display panel comprising a
flat, smooth substrate, an insulating layer formed on the inner surface of
the substrate, and reflective electrodes formed on the insulating layer,
comprises the steps of forming and drying an insulating, photosensitive
resin layer over the inner surface of the substrate, exposing the dried
photosensitive resin layer to light through a transparent mask having a
surface provided with minute irregularities, subjecting the exposed
photosensitive resin layer to a developing process and drying the
developed photosensitive resin layer to form an insulating resin layer
having a surface provided with minute irregularities, and depositing a
metal in a reflective film on the surface of the insulating resin layer.
According to a fourth aspect of the present invention, a method of
fabricating a reflection-type liquid crystal display panel comprising a
substrate, TFTs formed on the inner surface of the substrate, an
insulating layer formed on the inner surface of the substrate, and
reflective electrodes formed on the insulating layer, comprises the steps
of forming and drying an insulating, photosensitive resin layer over the
inner surface of the substrate, exposing the dried photosensitive resin
layer to light through a transparent mask having a surface provided with
minute irregularities, exposing the photosensitive resin layer to light
through a photomask provided with a contact hole pattern for forming
contact holes, subjecting the exposed photosensitive resin layer to a
developing process and drying the developed photosensitive resin layer to
form an insulating resin layer having a surface provided with minute
irregularities, and depositing a metal in a reflective film on the surface
provided with the minute irregularities of the insulating resin layer.
According to a fifth aspect of the present invention, a method of
fabricating a reflection-type liquid crystal display panel comprising a
flat, smooth substrate, an insulating layer formed on the inner surface of
the substrate, and a reflective electrode film formed on the insulating
layer in an electrode pattern, comprises the steps of forming and drying
an insulating, photosensitive resin layer over the inner surface of the
substrate, exposing the dried photosensitive resin layer to light through
a photomask having substantially the same pattern as the electrode
pattern, subjecting the exposed photosensitive resin layer to a developing
process and drying the developed photosensitive resin layer, depositing a
metal in a reflective thin film on the surface of the insulating resin
layer, and patterning the reflective thin film in the electrode pattern.
According to a sixth aspect of the present invention, a method of
fabricating a reflection-type liquid crystal display panel comprising a
substrate, TFTs formed on the inner surface of the substrate, an
insulating layer formed on the inner surface of the substrate, and a
reflective electrode film formed on the insulating layer in an electrode
pattern, comprises the steps of forming and drying an insulating,
photosensitive resin layer over the inner surface of the substrate,
exposing the dried photosensitive resin layer to light through a photomask
provided with a contact hole pattern for forming contact holes, subjecting
the exposed photosensitive resin layer to a developing process and drying
the developed photosensitive resin layer, and depositing a metal in a
reflection-type metal film on the surface of the insulating resin layer,
and patterning the reflective metal film in the electrode pattern.
The above and other objects, features and advantages of the present
invention will become more apparent from the following description taken
in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a typical sectional views of a reflection-type liquid crystal
display panel in a first embodiment according to the present invention;
FIG. 2 is a typical sectional views of a reflection-type liquid crystal
display panel in a second embodiment according to the present invention;
FIGS. 3A to 3F are typical sectional views explaining a method of
fabricating the reflection-type liquid crystal display panel shown in FIG.
1;
FIGS. 4A to 4G are typical sectional views explaining a method of
fabricating the reflection-type liquid crystal display panel shown in FIG.
2;
FIG. 5A is an enlarged typical sectional view of a portion including a
contact hole of the reflection-type liquid crystal display panel shown in
FIG. 2, taken on line VA--VA in FIG. 5B;
FIG. 5B is a typical plan view of the portion of the reflection-type liquid
crystal display panel shown in FIG. 5A;
FIG. 6 is a typical perspective view of a section including a contact hole
of the reflection-type liquid crystal display panel shown in FIG. 2;
FIG. 7 is a graph showing measured surface roughness of a ground glass
plate measured by a stylus-type profilometer;
FIG. 8 is a typical sectional views of a reflection-type liquid crystal
display panel in a third embodiment according to the present invention;
FIG. 9 is a typical sectional views of a reflection-type liquid crystal
display panel in a fourth embodiment according to the present invention;
FIG. 10 is a typical sectional views of a reflection-type liquid crystal
display panel in a fifth embodiment according to the present invention;
FIG. 11 is a typical sectional views of a reflection-type liquid crystal
display panel in a sixth embodiment according to the present invention;
FIGS. 12A to 12G are typical sectional views explaining methods of
fabricating the reflection-type liquid crystal display panels in the third
and the fifth embodiment according to the present invention;
FIGS. 13A to 13G are typical sectional views explaining methods of
fabricating the reflection-type liquid crystal display panels in the
fourth and the sixth embodiment according to the present invention;
FIG. 14 is a typical sectional view of a conventional monochromatic
reflection-type liquid crystal display panel; and
FIG. 15 is a typical sectional view of a conventional monochromatic
reflection-type liquid crystal display panel employing TFTs.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A reflection-type liquid crystal display panel according to the present
invention has a conductive metal thin film forming reflective electrodes
and formed on an insulating resin layer formed on the inner surface of a
back substrate and having a surface provided with minute irregularities.
Therefore, the conductive metal thin film has a shape precisely conforming
to the irregular surface of the insulating resin layer. Consequently,
external light falling on the conductive metal thin film from the front
side of the reflection-type liquid crystal display panel, namely, incident
light, is reflected irregularly and scattered, so that the reflection of
external matters in the reflection-type liquid crystal display panel is
suppressed. Reflection-type liquid crystal display panels embodying the
present invention and method of fabricating those liquid crystal display
panels will be described hereafter with reference to the accompanying
drawings.
Referring to FIG. 1 showing a reflection-type liquid crystal display panel
10 in a first embodiment according to the present invention, a back
substrate 10a, such as a glass substrate, and a front substrate 10b, such
as a glass substrate, are disposed opposite to each other; an insulating
layer 12 is formed over the inner surface of the back substrate 10a; first
electrodes 13a, namely, pixel electrodes, are formed on the insulating
layer 12 in the pattern of a spaced stripes; and an alignment film 14a is
formed over the insulating layer 12 so as to cover the first electrodes
13a. Second electrodes 13b are formed on the inner surface of the front
substrate 10b in the pattern of stripes perpendicular to the first
electrodes 13a, and an alignment film 14b is formed on the inner surface
of the front substrate 10b so as to cover the second electrodes 13b. The
second electrodes 10b on the front substrate 10b are transparent
electrodes. The first electrodes 13a are reflective electrodes of a
conductive metal for effective reflection. Although dependent on the size
of the panel and the number of pixels, the pitch of those electrodes
usually is on the order of 200 .mu.m.
The surface of the insulating layer 12 on which the first electrodes 13a
are formed is provided with minute irregularities 17. Since the first
electrodes 13a are formed by sputtering or the like in a small thickness
of 1 .mu.m or below, the shape of the surfaces of the first electrodes 13a
conforms to the irregular surface of the insulating layer 12 underlying
the first electrodes 13a. Since the first electrodes 13a have minutely
irregular surfaces, external matters in front of the front substrate 10b
of the reflection-type liquid crystal display panel will not be reflected
in the liquid crystal display panel.
The minute irregularities are minute ridges and valleys of magnitudes
capable of preventing the deterioration of the visibility of images
displayed on the liquid crystal display panel by the specular reflection
of external matters in the liquid crystal display panel. However, since
the irregularities are dependent on the thickness of a liquid crystal
layer 15, the thickness of the insulating layer 12 and the width of the
first electrodes 13a, the magnitudes of the irregularities cannot be
optionally determined. Usually, the thickness of the liquid crystal layer
15 is 10 .mu.m or below, and is in the range of 1 to 2 .mu.m if the liquid
crystal layer 15 is formed of a ferroelectric liquid crystal. Since the
thickness of the insulating layer 12 is on the order of several
micrometers, the height of ridges of the irregularities is 10 .mu.m at the
maximum to the wavelengths (400 to 750 nm) of visible radiations, i.e.,
0.4 to 0.75 .mu.m, at the minimum.
Referring to FIG. 2 showing a reflection-type liquid crystal display panel
10 in a second embodiment according to the present invention, a back
substrate 10a and a front substrate 10b are disposed opposite to each
other, an insulating layer 12 is formed over the inner surface of the back
glass substrate 10a, TFTs 11 and first electrodes 13a for applying a
voltage to a liquid crystal layer 15 are formed on the insulating layer
12, and an alignment film 14a is formed over the insulating layer 12 so as
to cover the TFTs 11 and the first electrodes 13a. A flat common electrode
13b is formed on the inner surface of the front substrate 10b, and an
alignment film 14b is formed on the inner surface of the front substrate
10b so as to cover the common electrode 13b. The common electrode 13b on
the front substrate 10b is a transparent electrode. The first electrodes
13a are reflective electrodes of a conductive metal for effective
reflection. The surface of the insulating layer 12 on which the first
electrodes 13a are formed is provided with minute irregularities 17. A
method of forming the first electrodes 13a and the magnitudes of minute
irregularities formed in the surfaces of the first electrodes 13a are the
same as those in the reflection-type liquid crystal display panel in the
first embodiment.
The insulating layer 12 insulates the first electrodes 13a from each other
and there is no particular restriction on material for forming the
insulating layer 12. However, it is desirable that minute irregularities
17 can be formed in the surface of the insulating layer 12 by a simple
process. Usually, a positive photosensitive resin which exhibits an
insulating property when dried is a suitable material for forming the
insulating layer 12. If the minute irregularities 17 are formed by a
mechanical means, such as sandblasting, the insulating layer 12 need not
be formed of a photosensitive material, but may be formed of an ordinary
insulating material, such as a polymeric material or silicon dioxide.
As is generally known, the back substrate 10a and the front substrate 10b
are spaced a predetermined distance apart by a spacer so as to form a
space between the alignment films 14a and 14b formed respectively on the
back glass substrate 10a and the front substrate 10b, and a liquid crystal
is filled in the space between the alignment films 14a and 14b to form a
liquid crystal layer 15, and the liquid crystal layer 15 is sealed in the
space by a sealing member 16 attached to the peripheral parts of the
substrates 10a and 10b.
FIG. 5A is an enlarged typical sectional view of a portion including a
contact hole of the reflection-type liquid crystal display panel in the
second embodiment shown in FIG. 2, taken on line VA--VA in FIG. 5B, and
FIG. 5B is a typical plan view of the portion of the reflection-type
liquid crystal display panel shown in FIG. 5A. Referring to FIGS. 5A and
5B, each of the TFTs 11 formed on the back substrate 10a is constituted of
an insulating layer 112 of silicon nitride (SN.sub.x), a semiconductor
layer 113 of amorphous silicon (a-Si), a gate electrode 111, a source
electrode 116, and a drain electrode 115 connected to the first electrode
13a. Usually, the gate electrodes 111 and the source electrode 116 are
formed perpendicularly to each other so as to form a matrix on the back
substrate 10a.
In this reflection-type liquid crystal display panel, the first electrodes
13a are connected through contact holes 30 formed in the insulating layer
12 to the drain electrodes 115. Referring to FIG. 6 showing a portion of
the reflection-type liquid crystal display panel in the second embodiment
around one of the contact holes 30, the first electrode 13a is connected
through the contact hole 30 formed in the insulating layer 12 to the drain
electrode 115. The first electrode 13a has a surface of a shape conforming
to the irregularities 17 formed in the surface of the insulating layer 12
to reflect incident light rays R falling thereon irregularly. Preferably,
the liquid crystal layer 15 is formed of a guest-host liquid crystal or a
polymer dispersion liquid crystal (PDLC).
A method of fabricating the reflection-type liquid crystal display panel in
the first embodiment of the present invention will be described with
reference to FIGS. 3A to 3F. As shown in FIG. 3A, the back substrate 10a
on which the reflective first electrodes 13a are to be formed is made. The
back substrate 10a may be a reflective substrate. The back substrate 10a
must be transparent if a reflecting layer is to be formed on its back
surface. Generally, the back substrate 10a is a flat, smooth glass plate.
The present invention is characterized by forming the reflective first
electrodes 13a on the insulating layer 12 of a resin having a surface
provided with the minute irregularities 17 and formed on the back
substrate 10a. There are some possible methods of forming the minute
irregularities 17. One of the methods of forming the minute irregularities
17 comprises the steps of forming a positive photosensitive resin layer on
the inner surface of the back substrate 10a, prebaking and drying the
positive photosensitive resin layer, closely superposing a flat
transparent sheet provided with minute irregularities on the
photosensitive resin layer, exposing the photosensitive resin layer to
light through the flat transparent sheet to produce minute irregularities
on the photosensitive resin layer. The flat transparent sheet having a
surface provided with minute irregularities may be a ground glass sheet or
a mat-finished plastic sheet.
Then, as shown in FIG. 3B, a positive photosensitive resin film for forming
the insulating layer 12 is formed over the inner surface of the back
substrate 10a. The positive photosensitive resin film is exposed to light
emitted by a light source 19 through a flat transparent sheet 18 provided
with minute irregularities 18a as shown in FIG. 3C. The thus exposed
positive photosensitive resin film is subjected to a developing step.
Consequently, portions of the positive photosensitive resin film exposed
to light and dissolvable in a developer are removed and the minute
irregularities 12m are formed in the positive photosensitive resin film to
complete the insulating layer 12 as shown in FIG. 3D. When the positive
photosensitive resin film is exposed to light through the transparent
sheet 18 provided with the minute irregularities 18a and the exposed
positive photosensitive resin film is developed, the minute irregularities
12m formed in the surface of the insulating layer 12 is not necessarily
exactly similar to the minute irregularities 18a of the transparent film
18. However, it is considered that ridges among the minute irregularities
18a of the transparent film 18 concentrate light rays and hence portions
of the positive photosensitive resin film corresponding to the ridges
among the minute irregularities 18a become more soluble than the rest of
the positive photosensitive resin film, so that the minute irregularities
12m are formed in the surface of the insulating layer 12 in a shape
substantially complementary to the minute irregularities 18a.
Materials suitable for forming the positive photosensitive resin film are,
for example, a mixture of a cresol novolac resin soluble in an alkaline
solution and naphthoquinone azide, and photosensitive acrylic resins. More
specifically, materials suitable for forming the positive photosensitive
resin film are, for example, OFPR-800, OFPR-5000, OFPR-8600, TSMR-8800 and
TSMR-CRB commercially available from Tokyo Oka Kogyo K.K. of Japan, AND
Optomer-PC302 commercially available from Japan Synthetic Rubber Co., Ltd.
of Japan.
As shown in FIG. 3E, a film of a conductive metal is formed on the surface
of the insulating layer 12 provided with the minute irregularities 12m to
form the first electrodes 13a. Usually, the film of a conductive metal is
an aluminum thin film formed by sputtering or the like. Since the
conductive metal thin film, i.e., an aluminum thin film, is formed in a
thickness of 1 .mu.m or below, the shape of the surface of the conductive
metal thin film is substantially the same as that of the surface of the
insulating layer 12 provided with the minute irregularities 12m. The
conductive metal thin film is patterned by an ordinary photoetching
process to form the first electrodes 13a in the shape of stripes as shown
in FIG. 3F. In FIG. 3F, the first electrodes 13a extend perpendicularly to
the sheet of paper.
The alignment films 14a and 14b are formed respectively on the substrates
10a and 10b, the substrates 10a and 10b are combined together so as to
form a space therebetween, a PDLC or a guest-host liquid crystal is filled
and sealed in the space between the substrates 10a and 10b to complete the
reflection-type liquid crystal display panel shown in FIG. 1.
A method of fabricating the reflection-type liquid crystal display panel in
the second embodiment of the present invention will be described with
reference to FIGS. 4A to 4G. As shown in FIG. 4A, the back substrate 10a
on which the reflective first electrodes 13a are to be formed is prepared.
The back substrate 10a is provided with the TFTs 11 on its inner surface.
The back substrate 10a may be a reflective substrate. The back substrate
10a must be transparent if a reflecting layer is to be formed on its back
surface. Generally, the back substrate 10a is a flat, smooth glass plate.
The reflective first electrodes 13a, similarly to those of the first
embodiment, are formed on the insulating layer 12 of a resin having a
surface provided with the minute irregularities 17 and formed on the back
substrate 10a. The minute irregularities 17 are formed by the same method
as that employed in forming the minute irregularities 17 of the first
embodiment.
A positive photosensitive resin film is formed on the inner surface of the
back substrate 10a as shown in FIG. 4B. A flat transparent sheet 18
provided with minute irregularities is superposed on the positive
photosensitive resin film, and the photosensitive resin film is exposed to
light emitted by a light source 19 through the flat transparent sheet 18
as shown in FIG. 4C. A photomask 17 provided with transparent parts at
positions corresponding to the TFTs 11 is superposed on the positive
photosensitive resin film as shown in FIG. 4D and the positive
photosensitive resin film is exposed to light through the photomask 17 to
form contact holes 30 in the positive photosensitive resin film as shown
in FIG. 4E. Then the thus exposed positive photosensitive resin film is
subjected to a developing step. Consequently, portions of the positive
photosensitive resin film exposed to light and dissolvable in a developer
are removed and the minute irregularities 12m and the contact holes 30 are
formed in the positive photosensitive resin film to complete the
insulating layer 12 as shown in FIG. 4E.
A film of a conductive metal is formed on the surface of the insulating
layer 12 provided with the minute irregularities 12m as shown in FIG. 4F
to form the first electrodes 13a. Usually, the film of a conductive metal
is an aluminum thin film formed by sputtering or the like. Since the
conductive metal thin film, i.e., an aluminum thin film, is formed in a
thickness of 1 .mu.m or below, the shape of the surface of the conductive
metal thin film is substantially exactly the same as that of the surface
of the insulating layer 12 provided with the minute irregularities 12m.
The conductive metal thin film is deposited also in the contact holes 30
to connect the drain electrodes of the TFTs to the first electrodes 13a.
The conductive metal thin film is patterned by an ordinary photoetching
process to form the first electrodes 13a in a matrix as shown in FIG. 4G.
The alignment films 14a and 14b are formed respectively on the substrates
10a and 10b, the substrates 10a and 10b are combined together so as to
form a space therebetween, a PDLC or a guest-host liquid crystal is filled
and sealed in the space between the substrates 10a and 10b to complete the
reflection-type liquid crystal display panel shown in FIG. 2.
EXAMPLE 1
A passive matrix reflection-type liquid crystal display panel in Example 1
will be described hereinafter.
(Back Panel)
A positive photosensitive acrylic resin (Optomer PC302 available from Japan
Synthetic Rubber Co., Ltd.) was spread by a spin coating method
(Rotational speed: 1500 rpm) on a flat glass substrate (Glass 7059
available from Corning Inc.) in a positive photosensitive film of about
1.5 .mu.m in thickness for forming an insulating layer 12 as shown in FIG.
3B. Then, the glass substrate was heated at 80.degree. C. for 60 sec on a
hot plate for prebaking.
A ground glass plate 18 (Ground Glass #1500 available from Koei Kagaku
K.K.) having a irregular surface was put on the positive photosensitive
film with the irregular surface thereof in close contact with the surface
of the positive photosensitive film, and then the positive photosensitive
film was exposed to light emitted by an extra-high pressure mercury lamp
(Power: 15 mW/cm.sup.2,
Wavelength: 405 nm) for 3 seconds (FIG. 3C).
Subsequently, the exposed positive photosensitive film was immersed in a
developing solution prepared by diluting PD523AD, a developer available
from Japan Synthetic Rubber Co., Ltd., 11.9 times for 90 seconds for
development (FIG. 3D). The entire surface of the positive photosensitive
film was exposed to light emitted by an extra-high pressure mercury lamp
(Power: 15 mW/cm.sup.2, Wavelength: 405 nm) for 30 seconds and then the
positive photosensitive film was heated at 220.degree. C. for 60 minutes
in an oven for postbaking. Consequently, an insulating layer 12 provided
in its surface with minute irregularities 12m substantially complementary
to the minute irregularities of the ground glass plate was completed.
A 0.2 .mu.m thick aluminum thin film was deposited by a sputtering process
over the insulating layer 12 as shown in FIG. 3E, and the aluminum thin
film was patterned by using a photomask to form stripe-shaped, 190 .mu.m
wide first electrodes 13a at intervals of 200 .mu.m as shown in FIG. 3F to
complete a back panel.
FIG. 7 is a graph showing measured surface roughness of the ground glass
plate measured by a stylus-type profilometer (Dektak 16000 available from
Dektak Inc.). A range of 500 .mu.m was measured. The arithmetical average
Ra of the surface roughness of the ground glass plate was 3192 .ANG.
(about 0.3 .mu.m), and the maximum height R.sub.max of ridges (maximum
depth of valleys) was about 22,000 .ANG. (about 2.2 .mu.m). In FIG. 7,
indicated at R is a position (106.38 .mu.m) where the sampling of measured
data for calculation is started and at M was a position (425.53 .mu.m)
where the sampling of measured data for calculation was ended.
(Front Panel)
A 0.15 .mu.m thick ITO film was deposited in stripes on a transparent glass
substrate (Glass 7059 available from Coring Inc.), i.e., a front substrate
10b, by a sputtering process to form transparent electrodes to be extended
perpendicularly to the first electrodes 13a of the back substrate 10a to
complete a front panel.
(Assembly of Liquid Crystal Display Panel)
Alignment films were formed on the inner surfaces of the front substrate
10b and the back substrate 10a, the front panel and the back panel were
disposed opposite to each other so as to form a space therebetween, and a
guest-host liquid crystal was filled and sealed in the space between the
front and the back panel to complete a liquid crystal display panel. When
the reflection-type liquid crystal display panel was driven, the liquid
crystal display panel lighted in white and displayed images in
satisfactory visibility.
Comparative Example 1
A liquid crystal display panel in Comparative example 1 was fabricated by
processes similar to those by which the liquid crystal display panel in
Example 1 was fabricated. The insulating layer of the liquid crystal
display panel in Comparative Example 1 was the same in material and
thickness as the insulating layer of the liquid crystal display panel in
Example 1, but minute irregularities were not formed in the surface of the
insulating layer of the liquid crystal display panel in Comparative
example 1, and hence the first electrodes formed on the insulating layer
having a smooth surface had specular surfaces. Other conditions for the
fabrication of the liquid crystal display panel in Comparative Example 1
were the same as those for the fabrication of the liquid crystal display
panel in Example 1. The first electrodes having the specular surfaces
reflected light intensely and the visibility of images displayed on the
liquid crystal display panel in Comparative Example 1 was inferior to that
of images displayed on the liquid crystal display panel in Example 1.
EXAMPLE 2
A TFT reflection-type liquid crystal display panel in Example 2 will be
described hereinafter.
(Back Panel)
A positive photosensitive acrylic resin (Optomer PC302 available from Japan
Synthetic Rubber Co., Ltd.) was spread by a spin coating method
(Rotational speed: 1500 rpm) on a flat glass substrate (Glass 7059
available from Corning Inc.) provided with TFTs on its inner surface in a
positive photosensitive film of about 1.5 .mu.m in thickness for forming
an insulating layer 12 as shown in FIG. 4B. Then, the glass substrate was
heated at 80.degree. C. for 60 seconds on a hot plate for prebaking.
A ground glass plate 18 (Ground Glass #1500 available from Koei Kagaku
K.K.) having the same irregular surface as that of the ground glass plate
employed in fabricating Example 1 was put on the positive photosensitive
film with the irregular surface thereof in close contact with the surface
of the positive photosensitive film, and then the positive photosensitive
film was exposed to light emitted by an extra-high pressure mercury lamp
(Power: 15 mW/cm.sup.2, Wavelength: 405 nm) for 3 seconds (FIG. 4C).
Subsequently, a photomask 17 provided with a contact hole pattern for
forming contact holes was superposed on the positive photosensitive resin
film as shown in FIG. 4D and the positive photosensitive film was exposed
to light emitted by an extra-high pressure mercury lamp (Power: 15
mW/cm.sup.2, Wavelength: 405 nm) for 15 seconds through the photomask 17
to form contact holes 30 for connecting the drain electrodes of the TFTs
to reflective first electrodes in the positive photosensitive film.
Then the exposed positive photosensitive film was immersed in a developing
solution prepared by diluting PD523AD, a developer available from Japan
Synthetic Rubber Co., Ltd., 11.9 times for 90 seconds for development
(FIG. 4E). Then, the entire surface of the positive photosensitive film
was exposed to light emitted by an extra-high pressure mercury lamp
(Power: 15 mW/cm.sup.2, Wavelength: 405 nm) for 30 seconds, and then the
positive photosensitive film was heated in an oven at 220.degree. C. for
60 minutes for postbaking. A 0.2 .mu.m thick aluminum film was formed on
the surface of the insulating layer 12 to form the first electrodes 13a by
a sputtering process. The aluminum film was patterned by an ordinary
patterning process to form the first electrodes 13a in a matrix as shown
in FIG. 4G to complete a back panel.
(Front Panel)
A common electrode was formed by depositing a 0.15 .mu.m thick ITO film
over a surface of a transparent glass substrate (Glass 7059 available from
Coring Inc.), i.e., a front substrate 10b, by a sputtering process to
complete a front panel.
(Assembly of Liquid Crystal Display Panel)
Alignment films were formed on the inner surfaces of the front substrate
10b and the back substrate 10a, the front panel and the back panel were
disposed opposite to each other so as to form a space therebetween, and a
guest-host liquid crystal containing a dichromatic dye was filled and
sealed in the space between the front and the back panel to complete a
liquid crystal display panel. When the reflection-type liquid crystal
display panel was driven, the liquid crystal display panel lighted in
white and displayed images in satisfactory visibility.
Comparative Example 2
A liquid crystal display panel in Comparative Example 2 was fabricated by
processes similar to those by which the liquid crystal display panel in
Example 2 was fabricated. The insulating layer of the liquid crystal
display panel in Comparative Example 2 was the same in material and
thickness as the insulating layer of the liquid crystal display panel in
Example 2, but minute irregularities were not formed in the surface of the
insulating layer of the liquid crystal display panel in Comparative
Example 2, and hence the first electrodes formed on the insulating layer
having a smooth surface had specular surfaces. Other conditions for the
fabrication of the liquid crystal display panel in Comparative Example 2
were the same as those for the fabrication of the liquid crystal display
panel in Example 2. The first electrodes having the specular surfaces
reflected light intensely and the visibility of images displayed on the
liquid crystal display panel in Comparative Example 2 was inferior to that
of images displayed on the liquid crystal display panel in Example 2.
In the foregoing reflection-type liquid crystal display panels of the
present invention, the first electrodes are provided in their surfaces
with the minute irregularities. Therefore the specular reflection of
images of external matters in front of the reflection-type liquid crystal
display panels does not occur, the external matters are not reflected in
the liquid crystal display panels, and hence the reflection-type liquid
crystal display panels are capable of displaying images in satisfactory
visibility.
The foregoing methods of fabricating a reflection-type liquid crystal
display panel are capable of easily fabricating liquid crystal display
panels capable of displaying images in satisfactory visibility.
A reflection-type liquid crystal display panel 10 in a third embodiment
according to the present invention will be described with reference to
FIG. 8, in which parts like of corresponding to those of the first
embodiment shown in FIG. 1 are designated by the same reference characters
and the description thereof will be omitted. As shown in FIG. 8, the
reflection-type liquid crystal display panel 10 has a back substrate 10a,
such as a glass substrate, and a front substrate 10b, such as a glass
substrate, disposed opposite to each other.
The reflection-type liquid crystal display panel in the third embodiment is
featured by the pattern of an insulating layer 12 underlying first
electrodes 13a being substantially the same as that of the first
electrodes 13a. The pattern of the insulating layer being substantially
the same as that of the first electrodes 13a signifies that the insulating
layer 12 is divided in isolated portions respectively corresponding to the
first electrodes 13a and does not mean that the respective patterns of the
insulating layer 12 and the first electrodes 13a are not perfectly
identical. Since the insulating layer 12 is divided into the isolated
portions, and the first electrodes 13a are formed respectively on the
isolated portions of the insulating layer 12, current leakage between the
first electrodes 13a can be suppressed.
A reflection-type liquid crystal display panel 10 in a fourth embodiment
according to the present invention will be described with reference to
FIG. 9, in which parts like of corresponding to those of the third
embodiment shown in FIG. 8 are designated by the same reference characters
and the description thereof will be omitted. As shown in FIG. 9, the
reflection-type liquid crystal display panel 10 has a back substrate 10a,
such as a glass substrate, and a front substrate 10b, such as a glass
substrate, disposed opposite to each other. TFTs for applying voltage to a
liquid crystal are arranged on the inner surface of the front substrate
10b, an insulating layer 12 is formed on the inner surface of the back
substrate 10a, and first electrodes 13a are formed on the insulating layer
12.
The liquid crystal display panel in the fourth embodiment is featured by
the pattern of the insulating layer 12 underlying first electrodes 13a
being substantially the same as that of the first electrodes 13a. Since
the insulating layer 12 is divided into the isolated portions, and the
first electrodes 13a are formed respectively on the isolated portions of
the insulating layer 12, current leakage between the first electrodes 13a
can be suppressed.
Reflection-type liquid crystal display panels 10 in fifth and sixth
embodiments according to the present invention will be described with
reference to FIG. 10 and 11, in which parts like of corresponding to those
of the third and the fourth embodiment shown in FIGS. 8 and 9 are
designated by the same reference characters and the description thereof
will be omitted.
The liquid crystal display panels in the fifth and the sixth embodiment are
substantially the same in configuration as those in the third and the
fourth embodiment shown in FIGS. 8 and 9, except that insulating layers 12
and the first electrodes 13a of the reflection-type liquid crystal display
panels in the fifth and the sixth embodiment, similarly to those of the
liquid crystal display panels in the first and the second embodiment shown
in FIGS. 1 and 2, are provided in their surfaces with minute
irregularities.
FIGS. 12A to 12G are views explaining methods of fabricating the
reflection-type liquid crystal display panels in the third and the fifth
embodiment. More precisely, FIGS. 12A to 12G are views explaining a method
of fabricating the liquid crystal display panel in the fifth embodiment
because the first electrodes 13a has surfaces provided with minute
irregularities as shown in FIG. 12G. However the method of fabricating the
liquid crystal display panel in the third embodiment is similar to that of
fabricating the liquid crystal display panel in the fifth embodiment only
except that the former has no step corresponding to that shown in FIG.
12C.
The back substrate 10a may be a reflective substrate. The back substrate
10a must be transparent if a reflecting layer is to be formed on its back
surface. Generally, the back substrate 10a is a flat, smooth glass plate.
The present invention is characterized by forming the reflective first
electrodes 13a on the insulating layer 12 of a resin having a surface
provided with the minute irregularities 17 and formed on the back
substrate 10a. There are some possible methods of forming the minute
irregularities 17. As mentioned previously, one of the methods of forming
the minute irregularities 17 comprises the steps of forming a positive
photosensitive resin layer on the inner surface of the back substrate 10a,
prebaking and drying the positive photosensitive resin layer, closely
superposing a flat transparent sheet provided with minute irregularities
on the photosensitive resin layer, exposing the photosensitive resin layer
to light through the flat transparent sheet to produce minute
irregularities on the photosensitive resin layer. The flat transparent
sheet having a surface provided with the minute irregularities may be a
ground glass sheet or a mat-finished plastic sheet.
Then a positive photosensitive film for forming the insulating layer 12 is
formed over the inner surface of the back substrate 10a as shown in FIG.
12B. The positive photosensitive film is exposed to light emitted by a
light source 19 through a flat transparent sheet 18 provided with minute
irregularities as shown in FIG. 12C. When the positive photosensitive film
is exposed to light through the transparent sheet 18 provided with the
minute irregularities, the minute irregularities 12m formed in the surface
of the insulating layer 12 is not necessarily exactly similar to the
minute irregularities of the transparent film 18. However, as mentioned
previously, it is considered that ridges among the minute irregularities
of the transparent film 18 concentrate light rays and hence portions of
the positive photosensitive film corresponding to the ridges among the
minute irregularities become more soluble than the rest of the positive
photosensitive film, so that the minute irregularities 12m are formed in
the surface of the insulating layer 12 in a shape substantially
complementary to the minute irregularities of the transparent film 18.
This step of forming the minute irregularities 12m in the insulating layer
12 shown in FIG. 12C is omitted from the method of fabricating the liquid
crystal display panel in the third embodiment, and hence the first
electrodes 13a of the liquid crystal display panel in the third embodiment
has flat surfaces.
As shown in FIG. 12D, the positive photosensitive film is exposed to light
through a photomask 17t. The area of each of portions of the thus
patterned insulating layer 12 may be either equal to or slightly larger
than that of the first electrodes 13a. It is obvious that portions of the
insulating layer 12 corresponding to marginal parts, i.e., peripheral
parts around a display part of the liquid crystal display panel, and
portions of the insulating layer 12 not having any connection with the
shape of the first electrodes 13 need not have the same shape as the first
electrodes 13. The thus exposed positive photosensitive film is subjected
to a developing process. Consequently, portions of the positive
photosensitive film exposed to light and dissolvable in a developer are
removed and the minute irregularities 12m are formed in the positive
photosensitive film to complete the insulating layer 12 as shown in FIG.
12E. It is obvious that the first electrodes 13 of the liquid crystal
display panel in the third embodiment has flat surfaces because the method
of fabricating the same does not include any step corresponding to that
shown in FIG. 12C.
An aluminum thin film, i.e., a thin film of a conductive metal, is formed
on the surface of the insulating layer 12 provided with the minute
irregularities 12m to form the first electrodes 13a as shown in FIG. 12F.
The aluminum thin film is patterned by an ordinary photoetching process to
form the first electrodes 13a in the shape of stripes as shown in FIG.
12G. In FIG. 12G, the first electrodes 13a extend perpendicularly to the
sheet of paper.
The alignment films 14a and 14b are formed respectively on the substrates
10a and 10b, the substrates 10a and 10b are combined together so as to
form a space therebetween, a PDLC or a guest-host liquid crystal is filled
and sealed in the space between the substrates 10a and 10b to complete the
reflection-type liquid crystal display panel shown in FIG. 10 (FIG. 8).
Method of fabricating the reflection-type liquid crystal display panels in
the fourth and the sixth embodiment of the present invention will be
described with reference to FIGS. 13A to 13G. More precisely, FIGS. 13A to
13G, similarly to FIGS. 12A to 12G being views explaining the method of
fabricating the liquid crystal display panel in the fifth embodiment, are
views explaining a method of fabricating the reflection-type liquid
crystal display panel in the sixth embodiment because the first electrodes
13a has surfaces provided with minute irregularities as shown in FIG. 13G.
As shown in FIG. 13A, the back substrate 10a on which the reflective first
electrodes 13a are to be formed is prepared. The back substrate 10a of the
sixth (fourth) embodiment, differing from the back substrate 10a of the
fifth (third) embodiment, is provided with the TFTs 11 on its inner
surface. The back substrate 10a may be a reflective substrate. The back
substrate 10a must be transparent if a reflecting layer is to be formed on
its back surface. Generally, the back substrate 10a is a flat, smooth
glass plate. In the sixth embodiment, the insulating layer 12, similarly
to the insulating layer 12 of the fourth embodiment, is provided with
minute irregularities in its surface, and the reflective first electrodes
13a are formed on the insulating layer 12 having the surface provided with
the minute irregularities.
A positive photosensitive film for forming the insulating layer 12 is
formed over the inner surface of the back substrate 10a as shown in FIG.
13B. The positive photosensitive film is exposed to light emitted by a
light source 18 through a flat transparent sheet 18 provided with minute
irregularities as shown in FIG. 13C. The step shown in FIG. 13C is omitted
for the reflection-type liquid crystal display panel in the fourth
embodiment. Subsequently, the insulating layer 12 is exposed to light
through a photomask 17 provided with a pattern 17t for forming isolated
portions of the insulating layer 12 divided by spaces 40 and a contact
hole pattern 17c for forming contact holes 30 for connecting the first
electrodes 13a to the TFTs 11 as shown in FIG. 13D. After the exposure
steps illustrated in FIGS. 13C and 13D (only the exposure step illustrated
in FIG. 13D for the fourth embodiment), the exposed positive
photosensitive film is subjected to a developing step to remove exposed,
dissolvable portions of the positive photosensitive film. Consequently,
the insulating layer 12 provided in its surface with the minute
irregularities 12m, divided into isolated portions by the spaces 40, and
provided with the contact holes 30 at positions corresponding to the TFTs
11 is formed as shown in FIG. 13E. The positive photosensitive film may be
exposed to light by two exposure steps, i.e., an exposure step employing a
photomask provided with the pattern 17t, and an exposure step employing
the photomask provided with the contact hole pattern 17c. Either the
exposure step employing the photomask provided with the pattern 17t or the
exposure step employing the photomask provided with the contact hole
pattern 17c may be executed first.
An aluminum thin film, i.e., a thin film of a conductive metal, for forming
the first electrodes 13a is formed over the surface of the insulating
layer 12 provided with the minute irregularities 12m. The aluminum thin
film is subjected to an ordinary photoetching step to form the first
electrodes 13a in a matrix as shown in FIG. 13G.
Then, the alignment films 14a and 14b are formed respectively on the
substrates 10a and 10b, the substrates 10a and 10b are combined together
so as to form a space therebetween, a PDLC or a guest-host liquid crystal
is filled and sealed in the space between the substrates 10a and 10b to
complete the reflection-type liquid crystal display panel shown in FIG. 11
(FIG. 9).
EXAMPLE 3
A passive matrix reflection-type liquid crystal display panel in Example 3
will be described hereinafter.
(Back Panel)
A positive photosensitive acrylic resin (Optomer PC302 available from Japan
Synthetic Rubber Co., Ltd.) was spread by a spin coating method
(Rotational speed: 1500 rpm) on a flat glass substrate (Glass 7059
available from Corning Inc.) in a positive photosensitive film of about
1.5 .mu.m in thickness for forming an insulating layer 12 as shown in FIG.
12B. Then, the glass substrate was heated at 80.degree. C. for 60 sec on a
hot plate for prebaking.
A photomask provided with a pattern of the first electrodes 13 was put on
the positive photosensitive film in close contact with the surface of the
positive photosensitive film, and then the positive photosensitive film
was exposed to light emitted by an extra-high pressure mercury lamp
(Power: 15 mW/cm.sup.2, Wavelength: 405 nm) for 15 seconds (FIG. 12D).
Subsequently, the exposed positive photosensitive film was immersed in a
developing solution prepared by diluting PD523AD, a developer available
from Japan Synthetic Rubber Co., Ltd., 11.9 times for 90 seconds for
development as shown in FIG. 12E. The entire surface of the thus developed
positive photosensitive film was exposed to light emitted by an extra-high
pressure mercury lamp (Power: 15 mW/cm.sup.2, Wavelength: 405 nm) for 30
seconds, and then the positive photosensitive film was heated at
220.degree. C. for 60 minutes in an oven for postbaking. Since the passive
matrix reflection-type liquid crystal display panel in Example 3 is a
trial piece of the liquid crystal display panel in the third embodiment,
the process shown in FIG. 12C was omitted.
A 0.2 .mu.m thick aluminum thin film was deposited by a sputtering process
over the insulating layer 12 as shown in FIG. 12F, and the aluminum thin
film was patterned by an ordinary patterning process using a photomask to
form stripe-shaped, 190 .mu.m wide first electrodes 13a at intervals of 10
.mu.m as shown in FIG. 12G to complete a back panel.
(Front Panel)
A 0.15 .mu.m thick ITO film was deposited over a surface of a transparent
glass substrate (Glass 7059 available from Coring Inc.), i.e., a front
substrate 10b, by a sputtering process to form a transparent second
electrodes in a predetermined pattern.
(Assembly of Liquid Crystal Display Panel)
Alignment films were formed on the inner surfaces of the front substrate
10b and the back substrate 10a, the front substrate panel and the back
panel were disposed opposite to each other so as to form a space
therebetween, and a guest-host liquid crystal containing 1.25% dichromatic
dye was filled and sealed in the space between the front and the back
panel to complete a liquid crystal display panel. When the reflection-type
liquid crystal display panel was driven, the liquid crystal was not
disturbed by leakage current, and the liquid crystal display panel lighted
in white and displayed images in satisfactory visibility.
Comparative Example 3
A reflection-type liquid crystal display panel in Comparative Example 3 was
fabricated by a method similar to that of fabricating the reflection-type
liquid crystal display panel in Example 3. The reflection-type liquid
crystal display panel in Comparative Example 3 was provided with a
continuous insulating layer which was not patterned into isolated
portions, an aluminum thin film of a thickness equal to that of the
aluminum thin film of Example 3 was formed on the insulating layer, the
aluminum thin film was patterned in stripe-shaped first electrodes having
a width equal to that of the first electrodes of the Example 3 and
arranged at a pitch equal to that of the first electrodes of Example 3.
Other conditions for fabricating the liquid crystal display panel in
Comparative Example 3 were the same as those for fabricating the liquid
crystal display panel in Example 3. When the reflection-type liquid
crystal display panel was driven, a large leakage current flowed between
the first electrodes, and the visibility of images displayed thereon was
inferior to that of images displayed on the reflection-type liquid crystal
display panel in Example 3.
EXAMPLE 4
A TFT reflection-type liquid crystal display panel in Example 4 will be
described hereafter.
(Back Panel)
A positive photosensitive acrylic resin (Optomer PC302 available from Japan
Synthetic Rubber Co., Ltd.) was spread by a spin coating method
(Rotational speed: 1500 rpm) on a back substrate 10a, i.e., a glass
substrate (Glass 7059 available from Corning Inc.) (FIG. 13A), provided
with TFTs 11 on its inner surface in a positive photosensitive film of
about 1.5 .mu.m in thickness for forming an insulating layer 12 as shown
in FIG. 13B. Then, the back substrate 10a was heated at 80.degree. C. for
60 seconds on a hot plate for prebaking.
A ground glass plate 18 (Ground Glass #1500 available from Koei Kagaku
K.K.) was put on the positive photosensitive film in close contact with
the surface of the positive photosensitive film, and then the positive
photosensitive film was exposed to light emitted by an extra-high pressure
mercury lamp 19 (Power: 15 mW/cm.sup.2, Wavelength: 405 nm) for 3 seconds
(FIG. 13C).
Subsequently, a photomask 17 provided with a contact hole pattern 17c for
forming contact holes and a pattern 17t for dividing the positive
photosensitive film (Width of electrodes: 190 .mu.m, Pitch of electrodes:
200 .mu.m, Intervals between electrodes: 10 .mu.m) was superposed on the
positive photosensitive film and the positive photosensitive film was
exposed to light emitted by an extra-high pressure mercury lamp (Power: 15
mW/cm.sup.2, Wavelength: 405 nm) for 15 sec through the photomask 17 (FIG.
13D) to form contact holes 30 for connecting the drain electrodes of the
TFTs to reflective first electrodes in the positive photosensitive film
and to divide the positive photosensitive film, i.e., an insulating layer
12, into isolated portions.
Then the exposed positive photosensitive film was immersed in a developing
solution prepared by diluting PD523AD, a developer available from Japan
Synthetic Rubber Co., Ltd., 11.9 times for 90 seconds for development
(FIG. 13E). Then, the entire surface of the positive photosensitive film
was exposed to light emitted by an extra-high pressure mercury lamp
(Power: 15 mW/cm.sup.2, Wavelength: 405 nm) for 30 seconds, and then the
positive photosensitive film was heated in an oven at 220.degree. C. for
60 minutes for postbaking to form the insulating layer 12. Minute
irregularities substantially complementary to those of the ground glass
plate were formed in the surface of the insulating layer 12. A 0.2 .mu.m
thick aluminum thin film was formed on the surface of the insulating layer
12 by a sputtering process as shown in FIG. 13E. The aluminum film was
patterned by an ordinary patterning process to form first electrodes 13a
as shown in FIG. 13G to complete a back panel.
(Front Panel)
A 0.15 .mu.m thick ITO film was deposited over a surface of a transparent
glass substrate (Glass 7059 available from Coring Inc.), i.e., a front
substrate 10b, by a sputtering process to form a common electrode.
(Assembly of Liquid Crystal Display Panel)
Alignment films were formed on the inner surfaces of the front substrate
10b and the back substrate 10a, the front panel and the back panel were
disposed opposite to each other so as to form a space therebetween, and a
guest-host liquid crystal containing 1.25% dichromatic dye was filled and
sealed in the space between the front and the back panel to complete a
liquid crystal display panel. When the reflection-type liquid crystal
display panel was driven, the liquid crystal was not disturbed by leakage
current and the liquid crystal display panel lighted in white and
displayed images in satisfactory visibility.
Comparative Example 4
A reflection-type liquid crystal display panel in Comparative Example 4 was
fabricated by a method similar to that of fabricating the reflection-type
liquid crystal display panel in Example 4. Although the insulating layer
of the Comparative Example 4 was provided minute irregularities in its
surface and was the same in material and thickness as the insulating layer
of the Example 4, the former was not divided into isolated portions. The
reflection-type liquid crystal display panel in Comparative Example 4 was
the same in other respects as the reflection-type liquid crystal display
panel in Example 4.
When the liquid crystal display panel was driven, leakage current flowed
between the first electrodes and the visibility of images displayed by the
liquid crystal display panel in Comparative Example 4 was inferior to that
of images displayed by the reflection-type liquid crystal display panel in
Example 4.
Although the invention has been described in its preferred embodiments with
a certain degree of particularity, obviously many changes and variations
are possible therein. It is therefore to be understood that the present
invention may be practiced otherwise than as specifically described herein
without departing from the scope and spirit thereof.
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